Through the high-resolution heat capacity, magnetic torque, and STS measurements on high-quality single crystals, we investigate the evolution of superconducting and normal state properties with \(x\)  in FeSe\(_{1-x}\) S\(_x\) . In Fig.REF (b), we show the phase diagram obtained by the heat capacity measurements. The drastic change in \(T_c\)  and superconducting fluctuations are found across \(x_c\) . To ensure the sample homogeneity, we used very small crystals (10-190 \(\mu \) g) for the thermodynamic measurements, and employed the long relaxation method with a home-made cell (Fig.REF (a)) designed for small single crystals. FiguresREF (b)-(e) depict the \(T\) -dependence of electronic heat capacity divided by \(T\) , \(C_{\rm e}/T\) , for \(x = 0\) , 0.05, 0.10 and 0.13. Here we subtract the phonon contribution, which shows \(T^3\) -dependence, as confirmed by the measurements in the normal state at high fields (Supplementary Materials). In Fig.REF (b), \(C_{\rm e}/T(T)\)  in FeSe (\(x=0\) ) exhibits an ordinary BCS-like jump at \(T_{\rm c}=9\)  K, consistent with the previous studies on larger samples [1]}, [2]}, [3]}. As the temperature is lowered below \(T_{\rm c}\) , \(C_{\rm e}/T\)  decreases with decreasing slope. Below \(\sim 3\)  K, \(C_{\rm e}/T\)  shows \(T\) -linear dependence, which is consistent with the strongly anisotropic superconducting gap [4]}, [3]}, [6]}. Similar \(C_{\rm e}/T(T)\)  is observed in orthorhombic phase \(x=\) 0.05, 0.10, and 0.13 with \(T_{\rm c}\)  of 9.7, 10 and 9.5 K, respectively (Figs.REF (c), (d) and (e)).
